A diesel engine may include glow plugs to heat air-fuel mixtures within the diesel engine so that engine starting during cold conditions may be improved. A glow plug in an engine cylinder may raise temperature within the engine cylinder so that an air-fuel mixture within the cylinder may ignite under increasing cylinder pressure as a piston in the cylinder approaches top dead center compression stroke. The glow plugs may be deactivated when the engine is warm and being restarted since the engine tends to heat the air-fuel mixture. Thus, it may be desirable to include glow plugs (e.g., electric heaters) in a diesel engine. However, it may not be possible to install glow plugs in some diesel engines because of the engine's configuration and because glow plugs typically protrude into engine cylinder. Therefore, it would be desirable to provide a way of cold starting a diesel engine without having to rely on glow plugs.
The inventor herein has recognized the above-mentioned disadvantages and has developed a diesel engine starting method, comprising: responsive to an engine start request, adjusting a supercharger having multiple drive ratios to a highest drive ratio, cranking an engine, and injecting fuel to the engine during cranking, where injecting fuel during engine cranking includes injecting an amount of fuel into engine cylinders during an engine cycle that provides for less than ten percent of energy in the injected fuel being released during the engine cycle.
By adjusting a supercharger drive ratio and injecting a small amount of fuel to engine cylinders during engine cranking in response to an engine start request; it may be possible to reliably cold start a diesel engine that does not include glow plugs. In particular, increasing the supercharger drive ratio may increase an amount of work performed on air entering engine cylinders, thereby increasing temperature in engine cylinders. Further, temperature within engine cylinders may be increased via low temperature heat released from the small amounts of fuel being injected. Instead of injecting larger amounts of cold fuel into engine cylinders and significantly chilling the air and fuel mixture in the engine cylinders, a small amount of fuel may be injected into a cylinder and that small amount of fuel may release heat into the cylinder when it is compressed without the small amount of fuel completely combusting. The heat added to the cylinder may be sufficient to facilitate combustion of a larger amount of fuel subsequently injected to the cylinder. Combustion of the larger amount of fuel may accelerate the engine crankshaft, thereby starting the engine. When less than ten percent of fuel injected combusts, a higher percentage of fuel injected participates in a first phase of two phase diesel fuel combustion than participates in the second phase of two phase diesel combustion so that cylinder heating may be improved.
The present description may provide several advantages. Specifically, the approach may allow for a diesel engine to be started without glow plugs during cold conditions. Further, in at least one example, charge in a cylinder may be heated without releasing significant exhaust emissions. In addition, the approach may apply different engine starting procedures for different low engine temperature engine starting conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.